Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS), astronomers at MIT have discovered a rocky exoplanet orbiting the bright K-dwarf star BD+05 4868A and observed variable transit depths that are characteristic of comet-like tails formed by dusty effluents emanating from a disintegrating planet. Unique to this exoplanet is the presence of prominent dust tails in both the trailing and leading directions that contribute to the extinction of starlight from the host star.
An artist’s impression of a disintegrating exoplanet around a giant star. Image credit: Jose-Luis Olivares, MIT.
BD+05 4868A, also known as TIC 466376085 or HIP 107587, lies approximately 140 light-years away in the constellation of Pegasus.
The newfound exoplanet, named BD+05 4868Ab, is about the mass of Mercury, although it circles about 20 times closer to the star than Mercury does to the Sun, completing an orbit every 30.5 hours.
At such close proximity to BD+05 4868A, the planet is roasting at around 1,600 degrees Celsius (3,000 degrees Fahrenheit) and is likely covered in magma that is boiling off into space.
As the planet whizzes around the star, it is shedding an enormous amount of surface minerals and effectively evaporating away.
MIT astronomer Marc Hon and colleagues discovered BD+05 4868Ab using NASA’s Transiting Exoplanet Survey Satellite (TESS).
The signal that tipped the astronomers off was a peculiar transit, with a dip that fluctuated in depth every orbit.
They confirmed that the signal is of a tightly orbiting rocky planet that is trailing a long, comet-like tail of debris.
“The extent of the tail is gargantuan, stretching up to 9 million km long, or roughly half of the planet’s entire orbit,” Dr. Hon said.
“It appears that the planet is disintegrating at a dramatic rate, shedding an amount of material equivalent to one Mount Everest each time it orbits its star.”
The researchers predict that the planet may completely disintegrate in about 1 million to 2 million years.
“We got lucky with catching it exactly when it’s really going away,” said Dr. Avi Shporer, an astronomer at MIT.
Of the nearly 6,000 planets that astronomers have discovered to date, scientists know of only three other disintegrating planets beyond our Solar System.
Each of these crumbling worlds were spotted over 10 years ago using data from NASA’s Kepler Space Telescope. All three planets were spotted with similar comet-like tails.
BD+05 4868Ab has the longest tail and the deepest transits out of the four known disintegrating planets to date.
“That implies that its evaporation is the most catastrophic, and it will disappear much faster than the other planets,” Dr. Hon said.
The team’s results will be published in the Astrophysical Journal Letters.
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Marc Hon et al. 2025. A Disintegrating Rocky Planet with Prominent Comet-like Tails around a Bright Star. ApJL, in press; arXiv: 2501.05431
